Cross-reference and incorporation by reference is made to commonly assigned co-pending application 08/134,775 and U.S. Pat. No. 5,339,139, both disclosing simplex and duplex document handlers.
The present invention relates to a document reproduction system which includes an improved document scanning system for automatically transporting documents to a document platen and for scanning the document to form line images at an image plane. More particularly, the invention relates to a scanning system capable of imaging documents in either a simplex or duplex mode of operation using sequentially enabled exposure stations.
There is extensive art on simplex or duplex document feeders used in light lens copiers and/or electronic (digital) printers which use a raster input scanner (RIS). This prior art is summarized in U.S. Pat. No. 5,339,139, referenced supra.
In the referenced prior art, a commonly used method of enabling a duplex document handling mode is to image a first (simplex) side at an exposure station and then to use an inverted mechanism to reverse the path of the document and bring the second (duplex) side into the same exposure station. See for example, U.S. Pat. No. 4,419,007. Inversion requires sheet movement changes and additional mechanisms to start and stop the inverted mechanism creating losses in productivity and also resulting in frequent document jams. Duplex scan systems are also known which expose both sides of a document while the document is moved along a continuous, non-inversion path. U.S. Pat. Nos. 4,571,636 (Itoh), 4,673,285 (Shogren) and 4,536,077 (Stoffel) all disclose use of two scan illumination stations, one for each side of the document, with the simplex and duplex scanned images following two optical paths but imaged onto the same image line. These references require a moving mirror (Stoffel or Itoh) or a moving lens (Shogen) to bring projected images onto a common imaging plane. U.S. Pat. No. 4,429,333 discloses a single exposure station, but it must move from a simplex side exposure station to a duplex exposure location. See also, Xerox Disclosure Journal Volume 8, Number 3, May/June 1983, page 263 which discloses use of two RIS stations to image both sides of the document. Moving optical components is undesirable because it can create optical misalignments and/or vibrations, is time consuming and requires precision mechanisms.
It is a feature of the disclosed embodiments to provide a duplex document imaging system which houses the document feeding and imaging components within a compact space. It is a still further feature to project simplex and duplex images at an image plane with a fixed optical system not requiring any movable components. It is a further operational feature to identify whether a simplex or duplex mode of operation is enabled and to provide an optimum feed path for either mode.
The disclosed embodiments include a scanning system with simplex and duplex modes of operation wherein two exposure stations are provided, one for each mode. Each exposure station projects line images along a optical path which includes one or two gradient index lens arrays for simplex or duplex operation, respectively. These lens arrays are characterized by having a short focal length and can be used in an optical system having a relatively short total conjugate thus enabling a compact optical unit. The lens array forms a focused, erect 1X image of a scanned document at an imaging plane. The gradient index lens arrays comprise a plurality of light conducting fibers made of glass or synthetic resin which has a refractive index distribution in a cross section thereof that varies parabolically outward from a center portion thereof. Each fiber acts as a focusing lens to transmit part of an image of an object placed near one end, e.g., each side of a document. An assembly of fibers, typically in a two row linear array, transmit and focus an image of the object. These fiber lenses may be those produced under the trade name "SELFOC", a mark registered in Japan and owned by the Nippon Sheet Glass Co., Ltd.
The embodiments are disclosed in a digital imaging system embodiment wherein simplex and duplex document sheets are circulated through an exposure zone by a CVT (constant velocity transport) document handling system and one or both sides are selectively and sequentially imaged onto a common linear sensor array. The document sheets may be controlled in (1 to N) serial order along a very short path in a continuous direction without the need for inversion of the sheet for duplex imaging.
Several embodiments are disclosed below which illustrate the application of the invention to accommodate various locations of a document feed tray appropriate for different overall machine designs.
More particularly, one feature relates to a document reproduction system for imaging both sides of duplex documents and for additionally imaging simplex documents, said document reproduction system including an automatic document feeding and imaging system for scanning both sides of document sheets and for projecting line images of the scanned document sides onto a light sensitive imaging member, said document feeding and imaging system comprising, in combination,
a first object plane, PA1 a first scanning station positioned beneath said first object plane, for scanning the first side of the document, said first scanning station including a first illumination system to illuminate a first exposure zone in said first object plane and further including a first lens system for projecting light reflected from said documents moving through said exposure zone as focused line images along a first optical path onto said light sensitive image member, PA1 a second object plane, PA1 a second scanning station positioned beneath said second object plane for scanning a second side of the document, PA1 said second scanning station including a second illumination system to illuminate a second exposure zone in said second object plane and further including a second lens system for projecting light reflected from documents moving through said second exposure zone along a second optical path superimposed with said first optical path onto said light sensitive member, PA1 a document feeding and control system for selectively feeding documents to be imaged at one of said first and second scanning stations in a simplex document mode of operation and through both said first and second scanning stations in a duplex document mode of operation, said control system selectively actuating said first and second illumination systems in response to said selected mode of operation. PA1 a first document scanning station for scanning a first side of the duplex documents, PA1 a first optical path for projecting line images of the first document side by a first projection lens onto said light sensitive imaging member, PA1 a second document scanning station for scanning a second side of the duplex documents, PA1 and a second optical path for projecting line images thereof by a second projection lens.
Further disclosed features, individually or in combination, include, in the document reproduction system described above, the use of linear gradient index lens arrays as the first and second lens systems and a linear light sensor array as the light sensitive member. A further feature is that the first gradient index lens array has a field capability in the cross array direction as large or larger than the second gradient index lens array. As a still further feature, the first and second illumination systems described above are incrementally illuminated by said control system for scanning a document, moving through said first and second exposure zones and wherein the illumination level of the second illumination system associated with the second scanning station is the same or higher than the first illumination system. There is also disclosed a document feeding and imaging apparatus for sequentially scanning both sides of sequentially fed duplex documents and for projecting line images thereof along an optical path onto a light sensitive imaging member comprising, in combination,
Further disclosed features, individually or in combination, include, in the document feeding and imaging apparatus described above, control of said first and second document scanning stations to alternatively provide linear feeding therethrough and imaging of simplex documents. A further feature is that the first document scanning station is a minor portion of the upper surface of a conventional fixed glass platen of a document reproduction apparatus. A still further feature is that said first and second document scanning stations are vertically superposed. A still further feature is that a single inversion loop document feeding path interconnects said first and second document scanning stations. Another feature is that the document line images from one said scanning station pass through the other said scanning station by optical alignment of said first and second projection lenses. An additional feature is the inclusion of a document feeding path wherein both simplex and duplex documents are moved therethrough without stopping. A still further feature is a document input feeder feeding directly into one of said first and second document scanning stations without inversion from a closely adjacent stack thereof in forward serial order. Another feature is that all optical imaging elements thereof are fixed in position for imaging of both simplex and duplex documents. A further feature is a field lens positioned in a minor portion in a field of said second gradient index lens array.